WO2010113953A1 - Method for producing seamless steel pipe - Google Patents
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- WO2010113953A1 WO2010113953A1 PCT/JP2010/055713 JP2010055713W WO2010113953A1 WO 2010113953 A1 WO2010113953 A1 WO 2010113953A1 JP 2010055713 W JP2010055713 W JP 2010055713W WO 2010113953 A1 WO2010113953 A1 WO 2010113953A1
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
- C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
- C21D9/085—Cooling or quenching
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/11—Making amorphous alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
Definitions
- the present invention relates to a method for producing a low alloy steel seamless steel pipe, and more particularly to a method for producing a low alloy steel seamless steel pipe having excellent toughness in direct quenching or in-line heat treatment, and preventing the occurrence of delayed fracture in the production process. It relates to a manufacturing method that can be used.
- in-line heat treatment means a method in which quenching is performed after soaking the steel pipe after hot rolling at a temperature equal to or higher than the Ar 3 point in a furnace or the like without cooling.
- in-line heat treatment step the step of heating the steel pipe in a furnace or the like and performing post-quenching
- the method is referred to as “in-line heat treatment method”.
- Seamless steel pipes are widely used mainly in application fields such as OCTG (Oil Country Tubular Goods) and line pipes that require high performance for corrosion resistance and toughness due to their reliability. Seamless steel pipes made from these materials are also used in these fields of application.
- heat treatment such as quenching and tempering is often performed after hot pipe making.
- a steel pipe once cooled after completion of hot pipe making is reheated to an Ac 3 transformation point or higher in an off-line heat treatment furnace, quenched, and further below an Ac 1 transformation point. It was common to temper at a temperature of (reheat quenching method).
- the steel pipe immediately after hot pipe making is directly quenched from the Ar 3 transformation point or higher using the retained heat of the steel pipe after hot pipe making, and then tempered.
- the process (direct quenching) has also been studied and improved.
- Patent Document 1 a continuously cast billet of a low alloy steel having a specific composition is processed into a seamless steel pipe at a temperature equal to or higher than the Ac 3 transformation point, and after direct quenching, the steel pipe is converted from the Ac 3 transformation temperature to the Ac 3 transformation temperature.
- a method for producing a high-strength steel pipe excellent in resistance to sulfide stress corrosion cracking comprising a step of reheating to a temperature range of + 100 ° C. and quenching again from that temperature, followed by a step of tempering at a temperature below the Ac 1 transformation point.
- reheat quenching is introduced before tempering in the simple direct quenching method, and compared to the simple direct quenching method, the resistance to sulfide stress corrosion It is said that the sex will be improved.
- Patent Document 2 is a method for producing a high-strength steel pipe comprising a step of performing reheating and quenching after direct quenching, as in Patent Document 1, and after direct quenching, tempering and precipitation under specific conditions. What controls carbides is disclosed.
- Patent Document 3 a billet of a low alloy steel having a specific composition is hot-drilled and rolled to produce a seamless steel pipe. Performed at a finish temperature of 800-1050 ° C, then “re-heated” under specific conditions in the temperature range of 850-1100 ° C., immediately followed by “direct quenching”, then tempered at a temperature below the Ac 1 transformation point.
- SSC resistance sulfide stress cracking resistance
- Patent Document 3 reheating in claim 1 of Patent Document 3 is not reheating from room temperature, but is performed between the steps of finish rolling and direct quenching, and is referred to as “ It is equivalent to “supplement heat”. This “reheating” is said to contribute to the refinement of crystal grains as a recrystallization process.
- the term “direct quenching” is used, but the process up to “Direct quenching” in Patent Document 3 corresponds to the in-line heat treatment referred to in this specification. That is, Patent Document 3 relates to a technique for improving an in-line heat treatment method, or a technique combining reheating and quenching with an in-line heat treatment process.
- Patent Document 4 after piercing and rolling at a specific strain rate, a specific average strain rate and a workability of 40% or more, and a finish are obtained by a rolling mill group in which a continuous stretch rolling mill and a finish rolling mill are arranged close to each other. After rolling at a temperature of 800 to 1050 ° C., quenching is performed at a cooling rate of 80 ° C./min or more to a temperature below the Ar 3 transformation point, and the cooled steel pipe is reheated to 850 to 1000 ° C. and then quenched. And the manufacturing method of the seamless steel pipe which implements the tempering process successively sequentially is indicated.
- the process is performed in a series of continuous lines. After completion of hot finish rolling, the steel pipe is once cooled to the Ar 3 transformation point or less (however, the cooling is stopped in the middle), and thereafter Reheating is characterized in that a reverse transformation from a ferrite phase having a body-centered cubic structure (BCC) to an austenite phase having a face-centered cubic structure (FCC) is caused.
- BCC body-centered cubic structure
- FCC face-centered cubic structure
- direct quenching or in-line heat treatment combined with heat treatment that combines reheat quenching (or further tempering) and direct quenching or in-line heat treatment (hereinafter referred to as “direct quenching”).
- direct quenching Many improved techniques have been disclosed.
- Patent Document 4 it is efficient to manufacture seamless steel pipes in a series of continuous lines.
- the invention of Patent Document 4 is to be implemented, a large amount of capital investment is required, and at the same time, there is a problem that constraints such as treatment time in each process unit occur due to the continuous line.
- Patent Documents 1 to 3 are not necessarily production methods performed in a continuous line, so if there is a quenching facility for quenching on the exit side of the finishing mill of hot pipe making, or finishing If there is equipment for heating before the first quenching on the exit side of the rolling mill and there is a quenching equipment on the exit side, the heating furnace for quenching offline, the quenching equipment for quenching, and the tempering furnace It can be implemented by using together. That is, the methods disclosed in Patent Documents 1 to 3 can be easily implemented by partially remodeling or diverting existing facilities as compared with the method disclosed in Patent Document 4.
- the object of the present invention is to produce a low alloy steel seamless steel pipe that is heat-treated by off-line re-quenching and tempering a steel pipe that has been quenched by direct quenching, etc., without adversely affecting product performance.
- Another object of the present invention is to provide a method for producing a seamless steel pipe capable of suppressing the occurrence of delayed fracture such as cracks and cracks.
- the inventors of the present invention obtained the knowledge shown in the following (a) to (f) as a result of intensive studies and experiments regarding means for suppressing impact cracking.
- the direct quenching is completed after the completion of the hot pipe production.
- the hardness of a seamless steel pipe should just be 42 or less by HRC, Preferably it is 41 or less, Most preferably, it is 40 or less.
- the present invention has been completed on the basis of the above-mentioned knowledge, and the gist thereof is a method for producing a seamless steel pipe as shown in the following (1) to (7).
- these may be simply referred to as “present invention (1)” to “present invention (7)”, respectively.
- the present invention (1) to the present invention (7) may be collectively referred to as “the present invention”.
- a method for producing a seamless steel pipe comprising quenching from a temperature equal to or higher than the point and tempering at a temperature equal to or lower than the Ac 1 transformation point.
- the heat treatment temperature in the heat treatment facility installed in direct connection with the quenching apparatus for direct quenching is 450 ° C. or more and the Ac 1 transformation point or less.
- a PL value defined by the following formula (1) satisfies a range of 14000 or more and 18600 or less.
- T the heat treatment temperature (° C.) and t is the heat treatment time (hr).
- the heat treatment temperature in the heat treatment equipment installed in direct connection with the quenching apparatus for direct quenching is over 500 ° C. and below the Ac 1 transformation point.
- a PL value defined by the following formula (1) satisfies a range of 14000 or more and 18600 or less.
- T the heat treatment temperature (° C.) and t is the heat treatment time (hr).
- a method for producing a seamless steel pipe characterized in that the steel pipe subjected to the heat treatment is further reheated and quenched from a temperature not lower than the Ac 3 transformation point and tempered at a temperature not higher than the Ac 1 transformation point.
- the heat treatment temperature in the heat treatment equipment installed in a manner connected to the quenching apparatus performing in-line quenching is 450 ° C. or more and the Ac 1 transformation point or less.
- a PL value defined by the following formula (1) satisfies a range of 14000 or more and 18600 or less.
- T the heat treatment temperature (° C.) and t is the heat treatment time (hr).
- the heat treatment temperature in the heat treatment equipment connected to the quenching apparatus for performing in-line quenching is over 500 ° C. and below the Ac 1 transformation point.
- a PL value defined by the following formula (1) satisfies a range of 14000 or more and 18600 or less.
- T the heat treatment temperature (° C.) and t is the heat treatment time (hr).
- composition of the billet contains at least one component selected from at least one of the following element groups (I) to (III) instead of a part of Fe: A method for producing a seamless steel pipe according to any one of the above (1) to (6).
- the present invention improves the product performance when manufacturing a low-alloy steel seamless steel pipe by heat-treating a directly quenched steel pipe or a steel pipe quenched by an in-line heat treatment method by offline reheating quenching and tempering. It is possible to suppress the occurrence of delayed fracture such as impact cracking and placement cracking without adverse effects.
- A. Chemical Composition of Low Alloy Steel The method for producing a seamless steel pipe according to the present invention is a process in which a billet having a specific low alloy steel composition is subjected to hot piercing and hot rolling, and further subjected to heat treatment. First, the chemical composition of the low alloy steel specified in the manufacturing method of the low alloy steel seamless steel pipe concerning this invention is demonstrated. In the following, “%” means “mass%”.
- C 0.15-0.35%
- C is an element necessary for improving the hardenability of the steel and improving the strength.
- the quenching effect is poor and sufficient strength cannot be obtained.
- the content exceeds 0.35%, the impact cracking resistance is remarkably lowered, and the effects of the present invention may not be sufficiently exhibited, and there is a possibility that the steel pipe is cracked only by the quenching operation. Therefore, the C content is set to 0.15% to 0.35%. Preferably it is 0.20 to 0.30%.
- Si 0.05 to 0.5% Si is an element that is necessary for deoxidation of steel and is effective in increasing the temper softening resistance and improving the SSC resistance. However, when it is excessively contained, it has the effect of embrittlement of the steel. For the purpose of deoxidation and SSC resistance improvement, it is necessary to contain 0.05% or more, but if it exceeds 0.5%, the toughness and SSC resistance are adversely affected. ⁇ 0.5%. Preferably, the content is 0.10 to 0.35%.
- Mn 0.1 to 1.5% Mn is contained for deoxidation and desulfurization of steel. However, if the content is less than 0.1%, the effect is poor. On the other hand, if the content exceeds 1.5%, the toughness and SSC resistance of the steel decrease. Therefore, the Mn content is set to 0.1 to 1.5%. Preferably it is 0.20 to 0.70%.
- Cr 0.2 to 1.5% Cr is an element that ensures the hardenability of the steel, improves the strength, and improves the SSC resistance. However, if the content is less than 0.2%, a sufficient effect cannot be obtained, and if it exceeds 1.5%, the toughness and the SSC resistance are reduced. Therefore, the content is made 0.2 to 1.5%. A preferable content of Cr is 0.3 to 1.0%.
- Mo 0.1 to 1.5% Mo increases the hardenability of the steel to ensure high strength and improves the temper softening resistance. As a result, high temperature tempering is possible, and it is effective in improving the SSC resistance. However, if the content is less than 0.1%, these effects are poor. On the other hand, if the content exceeds 1.5%, these effects are not only saturated, but also SSC resistance is deteriorated by segregation. Will be. Therefore, the content is 0.1 to 1.5%. A preferable content of Mo is 0.3 to 0.8%.
- Ti 0.005 to 0.50%
- Ti precipitates as fine carbonitride during the reheating temperature rise process for off-line quenching, and has the effect of preventing coarsening of crystal grains and abnormal grain growth during reheating and quenching.
- N which is an impurity in steel
- the hardenability of the steel is improved by allowing B to exist in the solid solution during quenching.
- the Ti content is set to 0.005 to 0.50%.
- the preferable content of Ti is 0.01 to 0.10%.
- Al 0.001 to 0.50%
- Al is an element effective for deoxidation of steel. However, if the content is less than 0.001%, the desired effect cannot be obtained. If the content exceeds 0.50%, inclusions increase and the toughness of the steel deteriorates. to degrade. Therefore, the content is made 0.001 to 0.50%.
- the chemical composition of the seamless steel pipe according to the present invention is such that the balance is Fe and impurities in addition to the above components.
- impurities are components that are mixed due to various factors in the manufacturing process, including raw materials such as ore and scrap, when industrially manufacturing seamless steel pipes, and have an adverse effect on the present invention. It means what is allowed in the range not given.
- Ni 0.1% or less Ni deteriorates the SSC resistance of the steel, and when its content exceeds 0.1%, the SSC resistance deteriorates remarkably. Therefore, the content of Ni as an impurity element is set to 0.1% or less.
- the upper limit of the content of P as an impurity element is set to 0.04%. Preferably it is 0.025% or less.
- the upper limit of the content of S as the impurity element is set to 0.01%. Preferably it is 0.005% or less.
- N 0.01% or less If N is present in excess, it tends to produce coarse inclusions together with Al, Ti, Nb, etc. to deteriorate the toughness and SSC resistance of the steel, and its content is 0.01 If it exceeds 50%, the toughness and SSC resistance deteriorate significantly, so the upper limit of the content of N as an impurity element is set to 0.01%. Further, if N is present excessively, the effect of improving the hardenability of B is hindered. Therefore, when adding B to the steel, it is desirable to fix N with Ti so as not to hinder the effect of adding B.
- O 0.01% or less O generates inclusions together with Al, Si, etc., and deteriorates the toughness and SSC resistance of the steel due to its coarsening.
- the content exceeds 0.01%, the deterioration of toughness and SSC resistance becomes significant. Therefore, the upper limit of the content of O as the impurity element is set to 0.01%.
- the chemical composition of the seamless steel pipe according to the present invention includes at least one selected from B, V, Nb, Ca, Mg, and REM (rare earth elements) as necessary in addition to the above components.
- B hydrogen
- Nb calcium
- Ca magnesium
- Mg magnesium
- REM rare earth elements
- B 0.01% or less B can be contained if necessary.
- B is an element that improves the hardenability of steel and improves the SSC resistance with a small amount of content. However, if the content exceeds 0.01%, the toughness and SSC resistance of the steel deteriorate. Therefore, the B content is 0.01% or less.
- the effect of B can be obtained even at 0.0001% or more, but in order to stably obtain the effect of B, it is preferable to contain 0.0005% or more.
- when there is little content of Ti and fixation of N by Ti is inadequate, since solid solution N couple
- V 0.5% or less
- V can be contained as necessary. If it is contained, it precipitates as fine carbide (VC) during tempering, increases the temper softening resistance, enables high-temperature tempering, and has the effect of improving SSC resistance.
- the combined addition with Nb has the effect of imparting greater sulfide stress cracking resistance to the steel, so it can be incorporated as required.
- the V content is 0.5% or less.
- the V content is 0.2% or less. In order to stably obtain the V content effect, it is preferable to set the content of V to 0.05% or more.
- Nb 0.4% or less Nb can be contained as necessary. If it is contained and processed after finish rolling, it precipitates as fine carbonitrides to prevent coarsening of crystal grains and abnormal grain growth during reheating and quenching. In addition, solute Nb precipitates finely as carbonitride during tempering after direct quenching, and has the effect of refining the prior austenite grain size and improving SSC resistance. Can do. However, if it exceeds 0.4%, the toughness of the steel deteriorates, so the Nb content is made 0.4% or less. Preferably, it is 0.1% or less. In order to stably obtain the Nb content effect, the Nb content is preferably 0.005% or more. The Nb content is more preferably 0.01% or more.
- Ca 0.005% or less
- Mg 0.005% or less
- REM 0.005% or less
- These elements can be contained as necessary. If any of them is contained, it reacts with S present as an impurity in steel to form a sulfide to improve the shape of inclusions, and has an effect of improving SSC resistance. At least one of these elements can be contained. However, when any element is contained in excess of 0.005%, not only the toughness and the SSC resistance are lowered, but also defects on the steel surface tend to occur frequently. For this reason, the content of these elements is 0.005% or less. Preferably, both are 0.003% or less. The upper limit of the total amount when two or more of these elements are contained is 0.005% or less, preferably 0.003% or less. In order to stably obtain the effects of containing these elements, it is preferable to contain 0.0001% or more of all of them.
- REM is a general term for 17 elements in which Y and Sc are combined with 15 elements of lanthanoid, and one or more of these elements can be contained. Note that the content of REM means the total content of these elements.
- the billet made of the above-mentioned low alloy steel is heated to a temperature range in which piercing can be performed and used for hot piercing.
- the billet has only to have the above-described chemical composition, and the history is not particularly limited, such as an ingot material, a bloom continuous cast material, and a round CC (Round Billet Continuous Casting) material.
- the billet heating temperature before drilling is usually in the range of 1100-1300 ° C.
- the means for hot drilling is not necessarily limited, but a hollow shell can be obtained by, for example, Mannesmann drilling.
- the obtained hollow shell is subjected to stretching and finishing.
- the drawing process is a step of producing a seamless steel pipe having a desired shape and size by drawing and adjusting the size of a hollow shell pipe punched by a punching machine, and can be performed by, for example, a mandrel mill or a plug mill.
- the finish rolling can be performed by a sizer or the like.
- the overall processing degree of the stretching process and the finishing process is not necessarily limited.
- the rolling finish temperature is preferably in the range of 1100 ° C. or lower. However, if the rolling finish temperature exceeds 1050 ° C., the crystal grain tends to be coarsened, so that the more preferable rolling finish temperature is 1050 ° C. or less. If the rolling temperature is 900 ° C. or lower, the processing may be somewhat difficult due to an increase in deformation resistance.
- quenching is performed immediately after completion of hot working.
- the quenching temperature must be at least the Ar 3 transformation point or higher. This is because at a temperature lower than the Ar 3 transformation point, the structure after direct quenching cannot be a martensite-based structure, and a predetermined strength cannot be obtained after another quenching.
- a quenching method general water quenching is economical, but a quenching method in which martensite transformation occurs is sufficient, and for example, mist quenching may be used.
- the steel pipe is heated in the furnace in the range of not less than the Ar 3 transformation point and not more than 1000 ° C.
- the heating is performed in the above range immediately before in-line quenching, a quenching temperature not lower than the Ar 3 transformation point can be sufficiently ensured by quenching immediately after the heat treatment in the furnace. .
- the quenching method is the same as in the case of the present invention (1) to (3).
- Heat treatment is performed at
- the heat treatment may be performed at a temperature equal to or lower than the Ac 1 transformation point in a heat treatment facility installed in connection with a quenching apparatus that performs the direct quenching or the like. It is a feature.
- this heat treatment step it is possible to reduce the hardness of the steel and prevent the occurrence of delayed fracture in the transport stage and storage state until the subsequent offline heat treatment (offline quenching) is performed. Therefore, for this purpose, not only the heat treatment is performed at a temperature below the Ac 1 transformation point, but the heat treatment is performed in a heat treatment facility installed in connection with a quenching apparatus that directly performs quenching or the like. It is necessary to be Therefore, performing the heat treatment at a temperature below the Ac 1 transformation point off-line requires transporting the quenched steel pipe for the heat treatment, and impact cracking in the transport stage. This is completely meaningless.
- the purpose of the heat treatment at a temperature below the Ac 1 transformation point is to adjust the hardness of the steel to 42 or less by HRC. It is preferably adjusted to 41 or less, more preferably adjusted to 40 or less. As a result, the occurrence of delayed fracture such as impact cracking and laying crack of the steel pipe is suppressed. Although the mechanism is not necessarily clear, this heat treatment also greatly improves the toughness of the steel pipe. Therefore, the improvement of toughness may contribute to the suppression of impact cracking.
- the heat treatment temperature of the heat treatment is less than 450 ° C.
- the heat treatment temperature of the heat treatment is more than 500 ° C.
- softening treatment in order to distinguish the heat treatment performed for the purpose of softening the steel pipe after the direct quenching or after the in-line quenching and before the reheating quenching from the tempering performed after the reheating quenching.
- the appropriate time for the heat treatment is a short time because of the nature of the heating device connected to the quenching device in the process of direct quenching or the like, which is performed continuously with the previous step. It is desirable that the heat treatment. From the viewpoint of preventing delayed fracture, long-time softening treatment is not excluded, but if it is short-time softening treatment, the equipment scale for that is small.
- the softening treatment time is preferably 1 to 300 minutes, more preferably 2 to 60 minutes.
- Softening treatment depends on the temperature of the softening treatment.
- the following equation (1) can be used as a Larson-Miller type parameter.
- T is a heat treatment (softening treatment) temperature (° C.)
- t is a heat treatment (softening treatment) time (hr)
- log I is a common logarithm.
- the softening treatment is preferably performed so that the PL value satisfies the range of 14000 to 18600.
- the PL value is 14000 or more, the hardness of the steel can be adjusted to 42 or less by HRC, and the impact cracking resistance can be further improved.
- the PL value is 18600 or less, the ⁇ grain size No. Of 8.5 (according to ASTM E-112-96; the same shall apply hereinafter) or more, the tendency to improve the SSC resistance becomes even more remarkable.
- the softening treatment is performed so that the PL value satisfies the range of 14000 to 18300.
- the ⁇ particle size No. Can be made 8.7 or more fine particles.
- the softening treatment is performed so that the PL value satisfies the range of 17000 to 18000.
- the ⁇ particle size No. Can be made fine particles of 8.8 or more, and the hardness of the steel can be adjusted to 40 or less by HRC.
- the prior austenite grain size after reheating and quenching tends to be larger than when the softening process is not performed.
- Ti or Nb carbonitride precipitates finely as the heat treatment temperature of the softening treatment increases and the heat treatment time increases. Since this carbonitride is partially agglomerated and coarsened during the reheating and quenching process, the pinning effect becomes incomplete at the soaking stage above the Ac 3 transformation point of reheating and quenching, and direct quenching. Later, it is considered that the prior austenite grain size after the final quenching becomes slightly larger than when no softening treatment is performed.
- the softening treatment is performed under the heating conditions necessary to make the steel hardness 42 or less, preferably 41 or less, and particularly preferably 40 or less in terms of HRC.
- Cooling after the softening treatment is preferably air cooling.
- the cooled steel pipe is reheated offline and quenched and then tempered.
- the reheating for off-line quenching needs to be at a temperature equal to or higher than the Ac 3 transformation point. Since the quenching process must be performed from the austenite state, the quenching temperature is ensured to be at least the Ar 3 transformation point. When the reheating temperature exceeds the Ac 3 transformation point + 100 ° C., the austenite grains become coarse, and therefore, it is desirable to set the heating temperature to the Ac 3 transformation point + 100 ° C. or less.
- Water quenching is generally used as the quenching method, but mist quenching may be used as long as it is a quenching method that causes martensitic transformation.
- the upper limit of the final tempering temperature is Ac 1 temperature as an upper limit in order not to precipitate austenite, but the lower limit of the tempering temperature may be changed according to the strength of the target steel pipe. When the strength is lowered, the temperature is increased, and when the strength is increased, the temperature is tempered at a lower temperature.
- ⁇ Cooling after the final tempering is preferably air cooling.
- Steel types A to C having the chemical composition shown in Table 1 were cast with a continuous casting machine to produce a billet having a diameter of 310 mm.
- the billet was heated to 1250 ° C. and then perforated by Mannesmann Piercer. Then, it was finished to a pipe making size of outer diameter 273.05 mm ⁇ thickness 19.05 mm ⁇ length 12 m by drawing rolling with a mandrel mill and reducing diameter rolling with a reducer.
- the hot rolling finish rolling temperature was 950 ° C.
- the steel pipe that has finished after hot rolling is (a) direct quenching by water quenching as it is, (b) in-line heat treatment in which after the hot rolling is completed, heat supplementation is immediately performed at 950 ° C. ⁇ 10 min, and quenching is performed by water cooling. Did either.
- Table 2 shows the conditions for the softening treatment. In Table 2, DQ indicates that (a) direct quenching was performed, and ILQ indicates that (b) inline heat treatment was performed.
- the water-cooled and quenched steel pipe was divided and heat-treated in various conditions in an experimental furnace. Further, quenching and tempering were performed in an experimental furnace simulating offline quenching and tempering. The heating conditions for quenching were 920 ° C., soaking time was 20 min, and quenching was water quenching. Final tempering is performed at a temperature of 680 ° C or more and Ac 1 point or less, soaking time is 30 to 60 min, and YS is adjusted to 90 ksi grade for steels A and B, and YS is adjusted to 110 ksi grade for steel C. I went.
- Survey items include hardness measurement and Charpy test at the stage after direct quenching and after softening treatment (compared to direct quenching after direct quenching and direct quenching). Went. That is, a part of the steel pipe that had been subjected to softening treatment after direct quenching or the like was taken as a test piece.
- the hardness was measured by using a Rockwell hardness meter, measuring the C scale hardness (HRC) at three points for each of the vicinity of the inner surface, the center of the wall thickness, and the vicinity of the outer surface, and the average value of nine points was calculated.
- HRC C scale hardness
- the Charpy test was cut in the L direction (the direction in which the longitudinal direction was parallel to the rolling direction), and a 10 mm wide V-notch test piece based on ASTM E-23 was prepared.
- the test was performed at room temperature, and the ductile fracture surface rate and the absorbed energy were evaluated.
- the remaining steel pipe from which the above test specimens were separated was further subjected to the above-described reheating quenching and tempering.
- the final austenite grain size and SSC resistance were investigated in the final steel pipe.
- the prior austenite grain size was investigated in accordance with ASTM E-112-96 by embedding a sample with a cross-section perpendicular to the rolling direction in a resin and corroding with a saturated aqueous solution of picric acid (Bechet-Beaujard method).
- No. 20 steel type A
- No. 27 is obtained by performing quenching and tempering by reheating after in-line heat treatment without performing softening treatment (shown as conventional method II in Table 2).
- no. 21 (steel type A) and 29 (Steel Type C) is listed to show the prior austenite grain size in the as-quenched state after in-line heat treatment (shown as a reference example in Table 2), and is quenched immediately after in-line heat treatment. And the prior austenite grain size obtained by the process of performing only tempering later is shown.
- FIG. 1 summarizes the relationship between the PL value and hardness for the results in Table 2. If the PL value is 14000 or more, it is considered that a hardness of HRC42 or less can be secured.
- the austenite grain size after reheating and quenching when quenching and tempering by reheating without performing softening treatment after direct quenching, for example, No. No. 12, former austenite grain size no. Is 9.3, after hot rolling, cooling without direct quenching and reheating quenching and tempering (No. 11, conventional method I) particle size No. The austenite grain size becomes finer than that of 8.4. However, as the softening temperature after direct quenching increases or the heat treatment time increases, the prior austenite grain size No. 1 after obtaining the final quenching is obtained. A tendency to decrease is observed.
- FIG. 2 summarizes the relationship between the PL value and the austenite ( ⁇ ) particle size after reheating and quenching (before final tempering) for the results in Table 2.
- the particle size no. I is 8.5 or more, preferably 8.7 or more.
- the PL value is 18600 or less, preferably 18300 or less.
- Steels D to H having the chemical compositions shown in Table 4 were cast with a continuous casting machine to produce billets with a diameter of 310 mm.
- the billet is heated to 1250 ° C, then drilled with Mannesmann Piercer, finished at a finishing rolling temperature of 950 ° C and finished with hot working, and has a outer diameter of 273.05 mm x wall thickness of 19.05 mm x length of 12 m. Finished to dimensions.
- Steel D was directly quenched by water cooling after finish rolling.
- the heat treatment apparatus installed after being connected to the quenching apparatus of the in-line heat treatment process is performed by performing heat treatment at 950 ° C. ⁇ 10 min and quenching with water cooling. The softening treatment was performed. Separately, some steel (steel F) was allowed to cool after the finish rolling for comparison.
- test materials were reheated in an offline heat treatment furnace, quenched (water-cooled), and further tempered. Tempering was performed in a temperature range of 680 ° C. or more and below the Ac 1 transformation point, adjusting YS to 95 ksi class for steels D to G and YS to 110 ksi class for steel H. In addition, about all the test materials, the austenite particle size of steel was measured by the same method as Example 1 in the stage before the said tempering.
- a round bar tensile test piece having a parallel part diameter of 6.36 mm and a distance between marked lines of 25.4 mm was taken in the rolling direction from the steel pipe manufactured in the above-described process, and subjected to a tensile test at room temperature, and SSC resistance.
- a DCB test piece having a thickness of 10 mm, a width of 25 mm, and a length of 100 mm was taken from each test material, and a DCB test was conducted according to NACE (National Association of Corrosion Engineers) TM0177-2005 method D.
- No. 52-53 and no. 56-61 is an example of the present invention, in which a softening treatment is performed in a heat treatment facility installed in line with the quenching apparatus after in-line heat treatment.
- ⁇ particle size No. Is at 8.7 or more K ISSC is, YS is in the test material of less than 110ksi 30.7ksi ⁇ in 1/2 or more, in the above test material 110ksi, was 24.8 ksi ⁇ in 1/2 or more.
- YS95ksi grade at K ISSC is 30 or more as SSC resistance, in the 110ksi class is required 24 or more, the SSC resistance required according to the present invention examples it is clear that is secured.
- No. No. 51 is obtained by performing quenching and tempering offline after direct quenching as a comparative material. If there is no problem of delayed fracture, the SSC resistance is excellent.
- No. 54-55 which is one of the prior arts, was subjected to reheating and quenching from as-rolled (as-rolled) after the end of hot rolling, but the SSC resistance of the example of the present invention is higher than these. It is clear that it is excellent.
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Abstract
Description
なお、この加熱処理は、加熱処理の温度に依存する。そして、Larson-Miller型のパラメータとして、次の(1)式を用いて、PL値を所定の範囲に調整するのが好ましい。これによって、鋼の硬度を満足できる範囲に調整することができる。
PL=[T+273]×[19.78+log(t)] ・・・(1)式
但し、Tは加熱処理温度(℃)、tは加熱処理時間(hr)、logは常用対数である。 (e) Then, after direct quenching, it was found that heat treatment in a specific range of conditions achieves both the original purpose of refinement of prior austenite grains and improvement of impact cracking resistance.
Note that this heat treatment depends on the temperature of the heat treatment. Then, it is preferable to adjust the PL value to a predetermined range using the following equation (1) as a Larson-Miller type parameter. Thereby, the hardness of the steel can be adjusted to a satisfactory range.
PL = [T + 273] × [19.78 + log (t)] (1) where T is a heat treatment temperature (° C.), t is a heat treatment time (hr), and log is a common logarithm.
但し、Tは加熱処理温度(℃)、tは加熱処理時間(hr)である。 PL = (T + 273) × [19.78 + log (t)] (1) where T is the heat treatment temperature (° C.) and t is the heat treatment time (hr).
但し、Tは加熱処理温度(℃)、tは加熱処理時間(hr)である。 PL = (T + 273) × [19.78 + log (t)] (1) where T is the heat treatment temperature (° C.) and t is the heat treatment time (hr).
但し、Tは加熱処理温度(℃)、tは加熱処理時間(hr)である。 PL = (T + 273) × [19.78 + log (t)] (1) where T is the heat treatment temperature (° C.) and t is the heat treatment time (hr).
但し、Tは加熱処理温度(℃)、tは加熱処理時間(hr)である。 PL = (T + 273) × [19.78 + log (t)] (1) where T is the heat treatment temperature (° C.) and t is the heat treatment time (hr).
本願発明にかかる継目無鋼管の製造方法は、特定の低合金鋼組成からなるビレットを熱間穿孔及び熱間圧延し更に熱処理を行う工程を経るものである。まず、本発明にかかる低合金鋼継目無鋼管の製造方法において特定される低合金鋼の化学組成について説明する。以下において、「%」は「質量%」を意味する。 A. Chemical Composition of Low Alloy Steel The method for producing a seamless steel pipe according to the present invention is a process in which a billet having a specific low alloy steel composition is subjected to hot piercing and hot rolling, and further subjected to heat treatment. First, the chemical composition of the low alloy steel specified in the manufacturing method of the low alloy steel seamless steel pipe concerning this invention is demonstrated. In the following, “%” means “mass%”.
Cは鋼の焼入性を高めて強度を向上するために必要な元素であるが、その含有量が0.15%以下では焼入効果が乏しく十分な強度が得られない。一方、0.35%を超えて含有すると耐衝撃割れ性が著しく低下し、本発明の効果が十分発現できない場合があり、また焼入操作のみで鋼管に焼き割れが生じるおそれが生じる。従って、Cの含有量を0.15%~0.35%とする。好ましくは0.20~0.30%である。 C: 0.15-0.35%
C is an element necessary for improving the hardenability of the steel and improving the strength. However, if its content is 0.15% or less, the quenching effect is poor and sufficient strength cannot be obtained. On the other hand, if the content exceeds 0.35%, the impact cracking resistance is remarkably lowered, and the effects of the present invention may not be sufficiently exhibited, and there is a possibility that the steel pipe is cracked only by the quenching operation. Therefore, the C content is set to 0.15% to 0.35%. Preferably it is 0.20 to 0.30%.
Siは鋼の脱酸に必要であり、焼戻軟化抵抗を高めて耐SSC性を向上するのに有効な元素であるが、過剰に含有させると鋼を脆化する作用を有する。脱酸と耐SSC性向上の目的からは0.05%以上含有させることが必要であるが、0.5%を超えると靱性と耐SSC性に悪影響を与えるので、その含有量を0.05~0.5%とする。好ましくは0.10~0.35%である。 Si: 0.05 to 0.5%
Si is an element that is necessary for deoxidation of steel and is effective in increasing the temper softening resistance and improving the SSC resistance. However, when it is excessively contained, it has the effect of embrittlement of the steel. For the purpose of deoxidation and SSC resistance improvement, it is necessary to contain 0.05% or more, but if it exceeds 0.5%, the toughness and SSC resistance are adversely affected. ~ 0.5%. Preferably, the content is 0.10 to 0.35%.
Mnは鋼の脱酸と脱硫のために含有させる。しかし、その含有量が0.1%未満ではその効果に乏しく、一方、1.5%を超えて含有させると鋼の靱性と耐SSC性が低下する。したがって、Mnの含有量を0.1~1.5%とする。好ましくは0.20~0.70%である。 Mn: 0.1 to 1.5%
Mn is contained for deoxidation and desulfurization of steel. However, if the content is less than 0.1%, the effect is poor. On the other hand, if the content exceeds 1.5%, the toughness and SSC resistance of the steel decrease. Therefore, the Mn content is set to 0.1 to 1.5%. Preferably it is 0.20 to 0.70%.
Crは鋼の焼入性を確保し、強度を向上するとともに耐SSC性を向上する元素である。しかし、その含有量が0.2%未満では充分な効果が得られず、1.5%を超えると靱性と耐SSC性がかえって低下することとなる。したがって、その含有量を0.2~1.5%とする。なお、Crの好ましい含有量は0.3~1.0%である。 Cr: 0.2 to 1.5%
Cr is an element that ensures the hardenability of the steel, improves the strength, and improves the SSC resistance. However, if the content is less than 0.2%, a sufficient effect cannot be obtained, and if it exceeds 1.5%, the toughness and the SSC resistance are reduced. Therefore, the content is made 0.2 to 1.5%. A preferable content of Cr is 0.3 to 1.0%.
Moは鋼の焼入性を高めて高強度を確保すると共に、焼戻軟化抵抗を向上させる結果、高温焼戻が可能となり、耐SSC性を向上するのに有効である。しかし、その含有量が0.1%未満ではこれらの効果に乏しく、一方、1.5%を超えて含有するとこれらの効果が飽和するだけでなく、偏析することによって逆に耐SSC性を劣化することとなる。したがって、その含有量を0.1~1.5%とする。なお、Moの好ましい含有量は0.3~0.8%である。 Mo: 0.1 to 1.5%
Mo increases the hardenability of the steel to ensure high strength and improves the temper softening resistance. As a result, high temperature tempering is possible, and it is effective in improving the SSC resistance. However, if the content is less than 0.1%, these effects are poor. On the other hand, if the content exceeds 1.5%, these effects are not only saturated, but also SSC resistance is deteriorated by segregation. Will be. Therefore, the content is 0.1 to 1.5%. A preferable content of Mo is 0.3 to 0.8%.
Tiは、オフライン焼入のための再加熱の昇温過程で微細な炭窒化物として析出して、結晶粒の粗大化並びに再加熱焼入れ時の異常粒成長を防止する効果がある。また、鋼中の不純物であるNを固定する作用があるので、鋼中にBを添加する場合には、焼入時にBを鋼中に固溶状態で存在させて鋼の焼入性を向上する作用がある。しかし、その含有量が0.005%未満ではこれらの効果が小さく、一方、0.50%を超えて含有すると鋼の靱性劣化を招くこととなる。従って、Tiの含有量を0.005~0.50%とする。なお、Tiの好ましい含有量は0.01~0.10%である。 Ti: 0.005 to 0.50%
Ti precipitates as fine carbonitride during the reheating temperature rise process for off-line quenching, and has the effect of preventing coarsening of crystal grains and abnormal grain growth during reheating and quenching. Also, since it has the effect of fixing N, which is an impurity in steel, when adding B to the steel, the hardenability of the steel is improved by allowing B to exist in the solid solution during quenching. Has the effect of However, if the content is less than 0.005%, these effects are small. On the other hand, if the content exceeds 0.50%, the toughness of the steel is deteriorated. Therefore, the Ti content is set to 0.005 to 0.50%. The preferable content of Ti is 0.01 to 0.10%.
Alは鋼の脱酸に有効な元素である。しかし、その含有量が0.001%未満では所望の効果が得られず、0.50%を超えると介在物が多くなって鋼の靱性が劣化し、介在物の粗大化により耐SSC性が劣化する。したがって、その含有量を0.001~0.50%とする。 Al: 0.001 to 0.50%
Al is an element effective for deoxidation of steel. However, if the content is less than 0.001%, the desired effect cannot be obtained. If the content exceeds 0.50%, inclusions increase and the toughness of the steel deteriorates. to degrade. Therefore, the content is made 0.001 to 0.50%.
Niは鋼の耐SSC性を劣化させ、その含有量が0.1%を超えると耐SSC性の劣化が著しくなる。したがって、不純物元素としてのNiの含有量を0.1%以下とする。 Ni: 0.1% or less Ni deteriorates the SSC resistance of the steel, and when its content exceeds 0.1%, the SSC resistance deteriorates remarkably. Therefore, the content of Ni as an impurity element is set to 0.1% or less.
Pは粒界に偏析して鋼の靱性と耐SSC性を劣化させ、その含有量が0.04%を超えると靱性と耐SSC性の劣化が著しくなる。したがって、不純物元素としてのPの含有量の上限を0.04%とする。好ましくは0.025%以下である。 P: 0.04% or less P segregates at the grain boundaries to deteriorate the toughness and SSC resistance of the steel. When the content exceeds 0.04%, the toughness and SSC resistance deteriorate significantly. Therefore, the upper limit of the content of P as an impurity element is set to 0.04%. Preferably it is 0.025% or less.
Sは粗大な介在物を生成して鋼の靱性と耐SSC性を劣化させる。その含有量が0.01%を超えると靱性と耐SSC性の劣化が著しくなる。したがって、不純物元素としてのSの含有量の上限を0.01%とする。 好ましくは0.005%以下である。 S: 0.01% or less S generates coarse inclusions and deteriorates the toughness and SSC resistance of steel. When the content exceeds 0.01%, the deterioration of toughness and SSC resistance becomes significant. Therefore, the upper limit of the content of S as the impurity element is set to 0.01%. Preferably it is 0.005% or less.
Nは過剰に存在すると、Al、Ti、Nb等とともに粗大な介在物を生成して鋼の靱性と耐SSC性を劣化させる傾向があり、その含有量が0.01%を超えると靱性と耐SSC性の劣化が著しくなるので、不純物元素としてのNの含有量の上限を0.01%とする。また、Nが過剰に存在すると、Bの焼入れ性向上効果を妨げるので、鋼中にBを添加する場合には、B添加の効果を妨げないように、TiによってNを固定することが望ましい。 N: 0.01% or less If N is present in excess, it tends to produce coarse inclusions together with Al, Ti, Nb, etc. to deteriorate the toughness and SSC resistance of the steel, and its content is 0.01 If it exceeds 50%, the toughness and SSC resistance deteriorate significantly, so the upper limit of the content of N as an impurity element is set to 0.01%. Further, if N is present excessively, the effect of improving the hardenability of B is hindered. Therefore, when adding B to the steel, it is desirable to fix N with Ti so as not to hinder the effect of adding B.
OはAl、Si等とともに介在物を生成し、その粗大化により、鋼の靱性と耐SSC性を劣化させる。その含有量が0.01%を超えると靱性と耐SSC性の劣化が著しくなる。したがって、不純物元素としてのOの含有量の上限を0.01%とする。 O: 0.01% or less O generates inclusions together with Al, Si, etc., and deteriorates the toughness and SSC resistance of the steel due to its coarsening. When the content exceeds 0.01%, the deterioration of toughness and SSC resistance becomes significant. Therefore, the upper limit of the content of O as the impurity element is set to 0.01%.
Bは必要に応じて含有させることができる。Bは微量の含有量で鋼の焼入性を向上し、耐SSC性を改善する元素である。しかし、0.01%を超えて含有させると、鋼の靱性と耐SSC性が劣化する。従って、Bの含有量を0.01%以下とする。なお、Bの効果は、0.0001%以上でも得られるが、Bの効果を安定的に得るためには、0.0005%以上含有させるのが好ましい。なお、Tiの含有量が少なく、TiによるNの固定が不十分な場合は、固溶NがBと結合してBNを形成するため、有効なB濃度が減少する。Bの添加量はTi及びNの含有量を考慮する必要がある。 B: 0.01% or less B can be contained if necessary. B is an element that improves the hardenability of steel and improves the SSC resistance with a small amount of content. However, if the content exceeds 0.01%, the toughness and SSC resistance of the steel deteriorate. Therefore, the B content is 0.01% or less. The effect of B can be obtained even at 0.0001% or more, but in order to stably obtain the effect of B, it is preferable to contain 0.0005% or more. In addition, when there is little content of Ti and fixation of N by Ti is inadequate, since solid solution N couple | bonds with B and forms BN, effective B density | concentration reduces. The addition amount of B needs to consider the contents of Ti and N.
Vは必要に応じて含有させることができる。含有させれば、焼戻時に微細な炭化物(VC)として析出して、焼戻軟化抵抗を高め、高温焼戻を可能とし、その結果、耐SSC性を向上する効果がある。特に、Nbとの複合添加で鋼に一層大きな硫化物応力割れ抵抗性を付与する作用があるので、必要に応じて含有させることができる。しかし、その含有量が0.5%を超えると鋼の靱性が劣化する。したがって、Vの含有量を0.5%以下とする。好ましくは、Vの含有量は0.2%以下である。なお、Vの含有効果を安定的に得るには、Vは0.05%以上の含有量とすることが好ましい。 V: 0.5% or less V can be contained as necessary. If it is contained, it precipitates as fine carbide (VC) during tempering, increases the temper softening resistance, enables high-temperature tempering, and has the effect of improving SSC resistance. In particular, the combined addition with Nb has the effect of imparting greater sulfide stress cracking resistance to the steel, so it can be incorporated as required. However, if its content exceeds 0.5%, the toughness of the steel deteriorates. Therefore, the V content is 0.5% or less. Preferably, the V content is 0.2% or less. In order to stably obtain the V content effect, it is preferable to set the content of V to 0.05% or more.
Nbを必要に応じて含有させることができる。含有させて仕上げ圧延後に処理を行えば、微細な炭窒化物として析出して結晶粒の粗大化並びに再加熱焼入時の異常粒成長を防止する。加えて、固溶Nbは直接焼入後の焼戻時に炭窒化物として微細に析出し、旧オーステナイト粒径を微細化し、耐SSC性を向上する効果があるので、必要に応じて含有させることができる。しかし、0.4%を超えると鋼の靱性が劣化するので、Nbの含有量を0.4%以下とする。好ましくは、0.1%以下である。なお、Nbの含有効果を安定的に得るには、Nb含有量を0.005%以上とするのが好ましい。Nb含有量を0.01%以上とすることがより好ましい。 Nb: 0.4% or less Nb can be contained as necessary. If it is contained and processed after finish rolling, it precipitates as fine carbonitrides to prevent coarsening of crystal grains and abnormal grain growth during reheating and quenching. In addition, solute Nb precipitates finely as carbonitride during tempering after direct quenching, and has the effect of refining the prior austenite grain size and improving SSC resistance. Can do. However, if it exceeds 0.4%, the toughness of the steel deteriorates, so the Nb content is made 0.4% or less. Preferably, it is 0.1% or less. In order to stably obtain the Nb content effect, the Nb content is preferably 0.005% or more. The Nb content is more preferably 0.01% or more.
これらの元素は、必要に応じて含有させることができる。いずれも、含有させれば、鋼中に不純物として存在するSと反応して硫化物を形成して介在物の形状を改善し、耐SSC性を向上させる作用があるので、必要に応じて、これらの元素のうちの少なくとも一種を含有させることができる。しかし、いずれの元素も0.005%を超えて含有させると、靱性および耐SSC性が低下するだけでなく、鋼表面に欠陥が多発しやすくなる。このため、これら元素の含有量は、いずれも0.005%以下とする。好ましくは、いずれも0.003%以下である。これらの元素を2種類以上含有させる場合の合計量の上限は0.005%以下であり、好ましくは0.003%以下である。なお、これらの元素の含有効果を安定的に得るには、いずれも0.0001%以上含有させるのが好ましい。 Ca: 0.005% or less, Mg: 0.005% or less, REM: 0.005% or less These elements can be contained as necessary. If any of them is contained, it reacts with S present as an impurity in steel to form a sulfide to improve the shape of inclusions, and has an effect of improving SSC resistance. At least one of these elements can be contained. However, when any element is contained in excess of 0.005%, not only the toughness and the SSC resistance are lowered, but also defects on the steel surface tend to occur frequently. For this reason, the content of these elements is 0.005% or less. Preferably, both are 0.003% or less. The upper limit of the total amount when two or more of these elements are contained is 0.005% or less, preferably 0.003% or less. In order to stably obtain the effects of containing these elements, it is preferable to contain 0.0001% or more of all of them.
本発明において、上記の低合金鋼からなるビレットは、穿孔可能な温度範囲に加熱され、熱間穿孔に供される。ビレットは上記の化学組成を有すればよく、インゴット材、ブルーム連続鋳造材、ラウンドCC(Round Billet Continuous Casting)材等、特に履歴は問われない。穿孔前のビレット加熱温度は、通常、1100~1300℃の範囲である。熱間穿孔の手段は必ずしも限定されるものではないが、例えば、マンネスマン穿孔等により中空素管を得ることができる。 B. About hot piercing, hot rolling, and heat treatment In the present invention, the billet made of the above-mentioned low alloy steel is heated to a temperature range in which piercing can be performed and used for hot piercing. The billet has only to have the above-described chemical composition, and the history is not particularly limited, such as an ingot material, a bloom continuous cast material, and a round CC (Round Billet Continuous Casting) material. The billet heating temperature before drilling is usually in the range of 1100-1300 ° C. The means for hot drilling is not necessarily limited, but a hollow shell can be obtained by, for example, Mannesmann drilling.
但し、Tは加熱処理(軟化処理)温度(℃)、tは加熱処理(軟化処理)時間(hr)、logは常用対数である。 PL = [T + 273] × [19.78 + log (t)] (1) where T is a heat treatment (softening treatment) temperature (° C.), t is a heat treatment (softening treatment) time (hr), log Is a common logarithm.
再加熱焼入後のオーステナイト粒度に関しては、直接焼入後軟化処理を行わずに、再加熱による焼入焼戻を行った場合、例えば、No.12では、旧オ-ステナイト粒度No.は9.3であり、熱間圧延後、直接焼入れを行わずに冷却し、再加熱焼入焼戻を行った場合(No.11、従来法I)の粒度No.の8.4と比較して、オーステナイト粒度が微細化する。しかし、直接焼入れ後の軟化処理温度の上昇または熱処理時間の長時間化に伴い、最終の焼入れを得た後の旧オーステナイト粒度No.が小さくなる傾向が認められる。 FIG. 1 summarizes the relationship between the PL value and hardness for the results in Table 2. If the PL value is 14000 or more, it is considered that a hardness of HRC42 or less can be secured.
Regarding the austenite grain size after reheating and quenching, when quenching and tempering by reheating without performing softening treatment after direct quenching, for example, No. No. 12, former austenite grain size no. Is 9.3, after hot rolling, cooling without direct quenching and reheating quenching and tempering (No. 11, conventional method I) particle size No. The austenite grain size becomes finer than that of 8.4. However, as the softening temperature after direct quenching increases or the heat treatment time increases, the prior austenite grain size No. 1 after obtaining the final quenching is obtained. A tendency to decrease is observed.
Claims (7)
- 質量%で、C:0.15~0.35%、Si:0.05~0.5%、Mn:0.1~1.5%、Cr:0.2~1.5%、Mo:0.1~1.5%、Ti:0.005~0.50%、Al:0.001~0.50%、残部Fe及び不純物からなり、不純物中のNiは0.1%以下、Pは0.04%以下、Sは0.01%以下、Nは0.01%以下、Oは0.01%以下の成分組成からなるビレットを熱間穿孔及び熱間圧延し更に熱処理を行う継目無鋼管の製造において、熱間圧延後の鋼管の温度がAr3変態点以上の温度から直接焼入を行い、その後、前記直接焼入を行う焼入装置に連接して設置された熱処理設備において450℃以上Ac1変態点以下の温度で加熱処理し、更に、前記加熱処理が施された鋼管を再加熱してAc3変態点以上の温度から焼入れ、Ac1変態点以下の温度で焼戻すことを特徴とする継目無鋼管の製造方法。 In mass%, C: 0.15 to 0.35%, Si: 0.05 to 0.5%, Mn: 0.1 to 1.5%, Cr: 0.2 to 1.5%, Mo: 0.1 to 1.5%, Ti: 0.005 to 0.50%, Al: 0.001 to 0.50%, balance Fe and impurities, Ni in impurities is 0.1% or less, P Is 0.04% or less, S is 0.01% or less, N is 0.01% or less, and O is 0.01% or less. In the manufacture of steelless pipes, in the heat treatment equipment installed directly connected to the quenching apparatus that performs quenching directly after the temperature of the steel pipe after hot rolling is higher than the Ar 3 transformation point. was heated at 450 ° C. or higher Ac 1 transformation point of the temperature, further, the heat treatment by reheating performed steel pipe Ac 3 transformation point Seamless steel pipe production method, characterized in that tempering from a temperature above quenching at Ac 1 transformation point or lower.
- 請求項1に記載の継目無鋼管の製造方法において、直接焼入を行う焼入装置に連接して設置された熱処理設備における加熱処理温度は、450℃以上Ac1変態点以下であって、かつ、下記(1)式で定義されるPL値が14000以上18600以下の範囲を満足するものであることを特徴とする製造方法。
PL=(T+273)X[19.78+log(t)] ・・・(1)式
但し、Tは加熱処理温度(℃)、tは加熱処理時間(hr)である。 The method of manufacturing a seamless steel pipe according to claim 1, the heat treatment temperature in the heat treatment equipment installed by connecting to a quenching apparatus for performing direct quenching is not more than Ac 1 transformation point 450 ° C. or higher, and A production method characterized in that the PL value defined by the following formula (1) satisfies a range of 14000 or more and 18600 or less.
PL = (T + 273) X [19.78 + log (t)] (1) where T is the heat treatment temperature (° C.) and t is the heat treatment time (hr). - 請求項2に記載の継目無鋼管の製造方法において、直接焼入を行う焼入装置に連接して設置された熱処理設備における加熱処理温度は、500℃を超えAc1変態点以下であって、かつ、下記(1)式で定義されるPL値が14000以上18600以下の範囲を満足するものであることを特徴とする製造方法。
PL=(T+273)×[19.78+log(t)] ・・・(1)式
但し、Tは加熱処理温度(℃)、tは加熱処理時間(hr)である。 In the method for producing a seamless steel pipe according to claim 2, the heat treatment temperature in the heat treatment equipment installed in connection with the quenching apparatus for performing direct quenching is over 500 ° C and below the Ac 1 transformation point, And the manufacturing method characterized by satisfy | filling the range whose PL value defined by following (1) Formula is 14000 or more and 18600 or less.
PL = (T + 273) × [19.78 + log (t)] (1) where T is the heat treatment temperature (° C.) and t is the heat treatment time (hr). - 質量%で、C:0.15~0.35%、Si:0.05~0.5%、Mn:0.1~1.5%、Cr:0.2~1.5%、Mo:0.1~1.5%、Ti:0.005~0.50%、Al:0.001~0.50%、残部Fe及び不純物からなり、不純物中のNiは0.1%以下、Pは0.04%以下、Sは0.01%以下、Nは0.01%以下、Oは0.01%以下の成分組成からなるビレットを熱間穿孔及び熱間圧延し更に熱処理を行う継目無鋼管の製造において、熱間圧延後の鋼管をインラインでAr3変態点以上1000℃までの温度で補熱し、Ar3変態点以上の温度からインライン焼入を行い、その後、前記インライン焼入を行う焼入装置に連接して設置された熱処理設備において450℃以上Ac1変態点以下の温度で加熱処理し、更に、前記加熱処理が施された鋼管を再加熱してAc3変態点以上の温度から焼入れ、Ac1変態点以下の温度で焼戻すことを特徴とする継目無鋼管の製造方法。 In mass%, C: 0.15 to 0.35%, Si: 0.05 to 0.5%, Mn: 0.1 to 1.5%, Cr: 0.2 to 1.5%, Mo: 0.1 to 1.5%, Ti: 0.005 to 0.50%, Al: 0.001 to 0.50%, balance Fe and impurities, Ni in impurities is 0.1% or less, P Is 0.04% or less, S is 0.01% or less, N is 0.01% or less, and O is 0.01% or less. in the production of steel pipe, heating complement at a temperature of the steel pipe after hot rolling to Ar 3 transformation point or higher 1000 ° C. inline performs inline quenching from Ar 3 transformation point or more of the temperature, then, the in-line quenching performing heating at a temperature of 450 ° C. or higher Ac 1 or less transformation point in the quenching apparatus the installed heat treatment equipment by concatenating Management, and further, the heat treatment by reheating performed steel pipe quenching from Ac 3 transformation point or above the temperature, seamless steel pipe production method, characterized by tempering at a temperature below the Ac 1 transformation point.
- 請求項4に記載の継目無鋼管の製造方法において、インライン焼入を行う焼入装置に連接して設置された熱処理設備における加熱処理温度は、450℃以上Ac1変態点以下であって、かつ、下記(1)式で定義されるPL値が14000以上18600以下の範囲を満足するものであることを特徴とする製造方法。
PL=(T+273)×[19.78+log(t)] ・・・(1)式
但し、Tは加熱処理温度(℃)、tは加熱処理時間(hr)である。 The method of manufacturing a seamless steel pipe according to claim 4, the heat treatment temperature in the heat treatment equipment installed by connecting to a quenching apparatus for performing in-line quenching is not more than Ac 1 transformation point 450 ° C. or higher, and A production method characterized in that the PL value defined by the following formula (1) satisfies a range of 14000 or more and 18600 or less.
PL = (T + 273) × [19.78 + log (t)] (1) where T is the heat treatment temperature (° C.) and t is the heat treatment time (hr). - 請求項5に記載の継目無鋼管の製造方法において、インライン焼入を行う焼入装置に連接して設置された熱処理設備における加熱処理温度は、500℃を超えAc1変態点以下であって、かつ、下記(1)式で定義されるPL値が14000以上18600以下の範囲を満足するものであることを特徴とする製造方法。
PL=(T+273)×[19.78+log(t)] ・・・(1)式
但し、Tは加熱処理温度(℃)、tは加熱処理時間(hr)である。 In the method for producing a seamless steel pipe according to claim 5, the heat treatment temperature in the heat treatment equipment installed in connection with the quenching apparatus for performing in-line quenching is more than 500 ° C and not more than the Ac 1 transformation point, And the manufacturing method characterized by satisfy | filling the range whose PL value defined by following (1) Formula is 14000 or more and 18600 or less.
PL = (T + 273) × [19.78 + log (t)] (1) where T is the heat treatment temperature (° C.) and t is the heat treatment time (hr). - ビレットの成分組成が、Feの一部に代えて、下記の(I)から(III)までの元素群のうちの少なくとも1群から選ばれた、少なくとも1種の成分を含有することを特徴とする、請求項1から6までのいずれかに記載の継目無鋼管の製造方法。
(I) B:0.01%以下。
(II) V:0.5%以下、Nb:0.4%以下。
(III) Ca:0.005%以下、Mg:0.005%以下、REM:0.005%以下。 The billet component composition contains at least one component selected from at least one of the following element groups (I) to (III) instead of a part of Fe: The method for producing a seamless steel pipe according to any one of claims 1 to 6.
(I) B: 0.01% or less.
(II) V: 0.5% or less, Nb: 0.4% or less.
(III) Ca: 0.005% or less, Mg: 0.005% or less, REM: 0.005% or less.
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AU2013228617B2 (en) * | 2012-03-07 | 2015-07-30 | Nippon Steel Corporation | Method for producing high-strength steel material having excellent sulfide stress cracking resistance |
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WO2019131037A1 (en) * | 2017-12-26 | 2019-07-04 | Jfeスチール株式会社 | Low alloy high strength seamless steel pipe for oil wells |
US11414733B2 (en) | 2017-12-26 | 2022-08-16 | Jfe Steel Corporation | Low-alloy high-strength seamless steel pipe for oil country tubular goods |
US11453924B2 (en) | 2017-12-26 | 2022-09-27 | Jfe Steel Corporation | Low-alloy high-strength seamless steel pipe for oil country tubular goods |
US11505842B2 (en) | 2017-12-26 | 2022-11-22 | Jfe Steel Corporation | Low-alloy high-strength seamless steel pipe for oil country tubular goods |
Also Published As
Publication number | Publication date |
---|---|
EA019610B1 (en) | 2014-04-30 |
AR075976A1 (en) | 2011-05-11 |
CA2752741A1 (en) | 2010-10-07 |
EA201171189A1 (en) | 2012-03-30 |
EP2415884A4 (en) | 2017-05-10 |
JP4632000B2 (en) | 2011-02-16 |
ES2721473T3 (en) | 2019-07-31 |
CA2752741C (en) | 2013-07-30 |
MX2011010385A (en) | 2012-01-19 |
UA101743C2 (en) | 2013-04-25 |
AU2010231626A1 (en) | 2011-09-08 |
CN102365376B (en) | 2013-10-23 |
JPWO2010113953A1 (en) | 2012-10-11 |
CN102365376A (en) | 2012-02-29 |
EP2415884B1 (en) | 2019-02-20 |
AU2010231626B2 (en) | 2013-03-07 |
US20120042992A1 (en) | 2012-02-23 |
US8696834B2 (en) | 2014-04-15 |
EP2415884A1 (en) | 2012-02-08 |
BRPI1012228A2 (en) | 2019-04-30 |
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